Production of a semiconductor device involves a step of forming an electroconductive film on a surface of a semiconductor wafer (hereinafter also referred to as a wafer) to form a wiring layer by photolithography, etching or the like; a step of forming an interlaminar insulating film on the wiring layer; and the like; and an uneven surface made of an electroconductive material such as metal and an insulating material is formed on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring have been advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique in which while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with an abrasive in the form of slurry having abrasive grains dispersed therein (hereinafter, referred to as slurry).
As shown in FIG. 1, a polishing apparatus used generally in CMP is provided, for example, with a polishing platen 2 for supporting a polishing pad 1; a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4; a substrate material for uniformly pressurizing a wafer; and a mechanism of feeding an abrasive 3. The polishing pad 1 is fitted with the polishing platen 2, for example, by sticking with a double-sided tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7, respectively, and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pressing the polished material 4 against the polishing pad 1.
When such CMP is conducted, there is a problem of judging the planarity of wafer surface. That is, the point in time when desired surface properties or planar state are reached is required to be detected. With respect to the thickness of an oxide film, polishing speed and the like, the following has been conventionally conducted that a test wafer is periodically treated, the results are confirmed, and thereafter a wafer to be a product is subjected to a polishing treatment.
In this method, however, the treatment time of a test wafer and the cost for the treatment are wasteful, and the test wafer not subjected to processing at all in advance and a product wafer are different in polishing results due to a loading effect unique to CMP, and accurate prediction of processing results is difficult without actual processing of the product wafer.
Accordingly, there has been a need in recent years for a method capable of in situ detection of the point in time when desired surface properties and thickness are attained at the time of CMP processing, in order to solve the problem described above. In such detection, various methods are used. From the viewpoints of measurement accuracy and spatial resolution in non-contract measurement, optical detection means comes to be used mainly.
The optical detection means is specifically a method of detecting the end-point of polishing by irradiating a wafer via a polishing pad through a window (light transmitting region) with light beam, and monitoring interference signal generated by reflection of the light beam.
As a method of detecting the end-point of polishing by such optical means, and a polishing pad used in the method, various methods and polishing pads have been proposed.
Conventional polishing pads for use in high-precision polishing are generally produced using a polyurethane resin foam sheet. Unfortunately, such a polyurethane resin foam sheet has insufficient cushioning properties and therefore can hardly apply uniform pressure to the entire surface of a wafer, though it has high local-planarization performance. In general, therefore, a soft cushion layer is additionally provided on the back side of such a polyurethane resin foam sheet, and the resulting laminated polishing pad is used for polishing.
However, conventional laminated polishing pads, which usually have a polishing layer and a cushion layer bonded together with a double-sided tape, have a problem in that a slurry can enter between the polishing layer and the cushion layer during polishing, so that the durability of the double-sided tape can decrease and delamination can easily occur between the polishing layer and the cushion layer.
Examples of proposed methods to solve this problem include the techniques described below.
Patent Document 1 discloses that a plastic film and a polishing pad are bonded together with a reactive hot-melt adhesive.
Patent Document 2 discloses a polishing pad including a base layer and a polishing layer bonded together with a hot-melt adhesive layer.
Patent Document 3 discloses a technique for forming a polishing pad including a polishing layer and a base layer bonded together with a double-sided tape, wherein a water blocking layer including a hot-melt adhesive is provided between the back side of the polishing layer and the double-sided tape to block a polishing slurry.
Patent Document 4 discloses a polishing pad including a polishing layer and a lower layer, which are bonded together with a hot-melt adhesive containing EVA.
Ply separation can be prevented by using a hot-melt adhesive. Unfortunately, when a hot-melt adhesive is used in the process of manufacturing a laminated polishing pad having a light transmitting region, the following problems can occur. (1) The manufacturing process can be complicated. (2) It can be difficult to place the light transmitting region at a desired position. (3) In the process of manufacturing the laminated polishing pad, the light transmitting region can be scratched or an adhesive layer or a resin film on the lower side of the light transmitting region can be scratched, or foreign particles can be deposited on the adhesive layer or the resin film, so that optical detection accuracy can decrease.